The current research proposal utilizes an animal model of spontaneous and persistent stereotype to study the neurobiological basis of abnormal repetitive behavior in humans. The spontaneous stereotyped behaviors emitted by deer mice are responsive to the environmental conditions associated with rearing. Recently, we have demonstrated that environmental enrichment functions to reduce the development and expression of stereotypic behavior in deer mice, yet the mechanisms underlying this outcome remain unknown. This proposal will attempt to identify the structural and functional brain changes responsible for this effect. First, alterations in neuronal metabolic activity will be assessed in order to identify those brain regions where altered neuronal activity is associated with reduced vulnerability to develop stereotype. Secondly, differences in dendritic spine density and branching patterns will be assessed as a potential mechanism for the effects of environmental enrichment on neuronal activity and dendritic alterations. Thus, the proposed studies will attempt to identify CNS changes associated with the environmental enrichment-related decrease in the development of stereotype behaviors in deer mice.